Across
- 1. a horizontal row of the periodic table
- 2. a chemical substance undergoing a chemical reaction
- 4. any substance that cannot be decomposed into simpler substances by ordinary chemical processes
- 6. a column in the periodic table of the chemical elements.
- 7. an uncharged elementary particle that has a mass nearly equal to that of the proton
Down
- 1. a particle that is identical to the nucleus and has a positive charge
- 3. a negatively charged subatomic particle
- 5. any hard surface that covers the outer surface of an organism.